# Devonian Armored Fish Fossil in China Bridges Jawless Lineage Evolutionary Gap Paleontologists describe Asioaspis brachyotus, revealing key anatomical shifts in ancient vertebrate history. - **Source:** [Sci.News: Breaking Science News](https://www.sci.news/) - **Published:** 2026-10-13 - **Topic:** [Business](https://brifing.si/c/business) - **Original article:** - **On Brifing:** https://brifing.si/s/ca574093-799b-43e6-8a94-c7869852af6e ## New Early Devonian Discovery Paleontologists have identified Asioaspis brachyotus, a new genus and species of armored jawless fish from southwestern China. Living approximately 419 million years ago during the Lochkovian stage, this species belongs to Galeaspida. This extinct group is phylogenetically closer to jawed vertebrates than modern lampreys or hagfish. ## Galeaspid Diversity and Importance Galeaspids remain central to understanding the evolutionary origin of key gnathostome traits, including jaws, spiracles, and paired appendages. Although geographically restricted to China and northern Vietnam, the Siluro-Devonian record contains 19 families, 74 genera, and 100 described species across two basal and three major taxonomic orders. ## Xishancun Formation Fossil Specimens The fossil material was excavated from the Xishancun Formation near Qujing in Yunnan province. Researchers collected three nearly complete headshields and three incomplete specimens. The oval headshields measure between 4.7 and 6 centimeters in maximum length, featuring distinct serrated edges and a coarse granular surface. ## Anatomical Headshield Morphology Diagnostic morphology includes a broad ventral rim and at least 12 pairs of gill pockets across the preserved headshields. These specific anatomical characteristics led paleontologists to classify Asioaspis brachyotus within the major order Polybranchiaspiformes, linking structural shield development directly to this widespread Early Devonian lineage. ## Evolutionary Diversification Dynamics The earliest known polybranchiaspiform genus, Platylomaspis, dates back approximately 438.6 million years. However, major diversification occurred during the Early Devonian epoch. The Xishancun Formation alone preserves nine genera and 15 distinct species, marking a critical evolutionary expansion phase within ancient benthic marine ecosystems. ## Sensory Opening Arrangement Shifts Unlike primitive relatives with tightly clustered eyes and dorsal openings on top of the headshield, Asioaspis brachyotus features widely spaced sensory apertures. These openings sit close to the ventral margin, exhibiting an intermediate structural configuration between early basal members and more advanced polybranchiaspiform families. ## Ecological Lifestyle Transition Evidence Primitive species relied on close-set dorsal openings for a semi-infaunal lifestyle partly buried in marine sand. In contrast, Asioaspis brachyotus could not burrow because sediment would flood its oralobranchial chamber. Researchers conclude it inhabited the seafloor surface, adopting a normal epibenthic ecological habit. ## Significance for Vertebrate Evolution Phylogenetic analysis places Asioaspis brachyotus directly between primitive and advanced lineages within Polybranchiaspiformes. This structural placement documents an evolutionary transition from semi-burrowing to surface-dwelling marine benthic habits. The findings refine existing anatomical timelines regarding how stem-gnathostome vertebrates adapted prior to major jawed diversification. ## Sources covering this story - https://www.sci.news/paleontology/asioaspis-brachyotus-15125.html — --- _Summary written by Brifing from the original reporting. Copyright in the original article belongs to its publisher; read the full piece at the link above._